1. Field of the Invention
The present invention relates to a gas fuel piping system and particularly, to a gas fuel piping system having a structure suited for inspection of leakage in the piping.
2. Description of the Related Art
Automobile, for example, has sometimes piping system for filling a fuel container or a tank with gas fuel and supplying a flow of the gas fuel from the fuel container to an engine. An example of a gas fuel container in the conventional piping systems for automobile is shown in FIG. 10 where compressed natural gas (CNG) is used as the fuel. As shown, the fuel container 1 filled with the CNG has a valve assembly 2 mounted in an inlet thereof. The valve assembly 2 includes a valve body or block member 3 in which a filling passage 4 and a supplying passage 5 are provided. The valve body 3 serves as a plug of the fuel container 1. A check valve 6 and a manual stop valve 7 are disposed across the filling passage 4 and the supplying passage 5, respectively. A solenoid valve 8 is mounted to an open end at the fuel container 1 side of the supplying passage 5 for opening and closing the open end. A CNG filling inlet 10 is provided on the outward end of a filling conduit 9 connected to the filling passage 4. Also, a check valve 11 is disposed in the filling inlet 10. The supplying passage 5 is joined to a supplying conduit 12 connected to an engine (not shown). The filling passage 4 and the supplying passage 5 are a couple of bores provided in the valve body 3 for communication with the filling conduit 9 and the supplying conduit 12 which are usually pipes connected with the bores, respectively.
For filling the fuel container 1 with the CNG, the solenoid valve 8 is closed to shut up the supplying passage 5. A flow of CNG is introduced to the filling inlet 10 and forced through the conduit 9 and the filling passage 4 to the fuel container 1. For supplying the CNG to the engine, the solenoid valve 8 is opened to clear the supplying passage 5. Upon the manual stop valve 7 being opened, the CNG is supplied through the supplying passage 5 and the conduit 12 to the engine. In case that the solenoid valve 8 is fault, the manual stop valve 7 is closed to stop the supply of CNG to the engine.
The inspection for leakage in the system is carried out as follows. For inspecting the filling conduit 9, the solenoid valve 8 is first closed, and then an inspection gas, namely a nitrogen gas, is fed from the filling inlet 10 to fill the system including the fuel container 1. Then, any change in the pressure in the conduit 9 is examined to judge whether or not a leakage occurs. For inspecting the supplying conduit 12, the manual stop valve 7 is closed and an inspection or nitrogen gas is introduced from a leakage inspection gas inlet (not shown) provided in the conduit 12. As the conduit 12 has been filled with the nitrogen gas, it is checked from change in the pressure whether or not a leakage occurs.
The valve assembly mounted in the CNG filling inlet may be different in arrangement from the above mentioned, in which the filling passage and the supplying passage are not separated from each other but integrally provided for common use. For example, a modification of the CNG valve assembly is disclosed in Japanese Patent Laid-open Publication No. (Hei)7-301359 where the filling passage and the supplying passage are not separated but integrally provided.
Those known valve assemblies however have following disadvantages. For inspecting the filling passage piping or the conduit 9, not only the conduit 9 but also the fuel container 1 have to be filled with the inspection gas. This will take an extra length of time for the filling and consume more time for removal of the inspection gas, hence hardly increasing the operational efficiency of the leakage inspection. Also, a large volume of the nitrogen gas is needed for the leakage inspection.